Vaccination or immunization is the most efficient measure to control infectious diseases in humans and in domestic animals. Also, in cancer immunotherapy, it is desired to stimulate an immune response against the tumor cells. Another application of immunization is in birth control. Sources of vaccine antigens include live attenuated or inactivated pathogens, and subunits, rDNA derived polypeptides, recombinant viruses, synthesized polypeptides and anti-idiotypes.
However, there are many diseases including AIDS and tropical diseases for which vaccines are not yet available or are not satisfactory. Similarly, immunotherapy is not a reliable method to treat tumors, in general.
Immunity to disease is due to the actions of specialized cells, especially the B and T lymphocytes. A basic description of the cellular basis of immunity may be found in Molecular Biology of the Cell (B. Alberts et al., Garland Publishing, Inc., New York, 1983). While the cellular basis of the immune system is understood in much greater detail than described in this reference, the basic principles can be clarified by its teachings, which state that the immune response is due primarily to the actions of specific cells, the B and T lymphocytes, which themselves consists of many subtypes. Virtually all lymphocyte responses are due to complex interactions among a variety of these and other cell types. In particular, the proliferation and differentiation of B and T cell effector cells and memory cells which underlies the desired objectives of immunization results from the interaction in the presence of the antigen between the class of T cells known as "Helper T cells" (Th) and either B lymphocytes or cytotoxic T cells. Also, the T cell recognition of antigens requires interaction with "antigen presenting cells" (APC) which incorporate antigen fragments into Type II MCH on the APC cell surfaces; APC cells include the B lymphocytes, macrophages, and the mast cells.
An addition, there are medical situations in which the suppression of immune reactions is desired; e.g., treatment of autoimmune diseases and allergies and in the transplantation of organs. In cellular terms, tolerance to antigen involves a class of T lymphocytes known as "Suppressor T cells" (Ts). The induction of immune tolerance is also within the scope of the instant invention.
This interaction between Th cells and other B or T cells is mediated by the production of hormonal factors known as lymphokines by Th cells which stimulate the growth and differentiation of effector and memory cells. The transmission of lymphokines from Th to target B or T cells is mediated by diffusion and takes place in the immediate vicinity of the Th-antibody interaction; sufficiently high concentrations of lymphokines to stimulate cell responses do not exist systemically. The interaction may also occur by synapse-like contacts between the cells. Monokines produced by the antigen presenting macrophages are also involved in the activation of T cells, representing another form immune cell communication by means of a soluble protein.
Generally, when killed organisms or their antigens are used for the vaccination or immunization the antigen is injected with a syringe into an appropriate body site. Thereafter, the T and B lymphocytes capable of recognizing the antigen may be attracted to the site of injection and interact with each other and with presenting cells such as mast cells there to produce the immune response. Alternatively, antigen can be transported in the lymphatic circulation to lymph nodes which are specialized organs which facilitate these cell-cell interactions with antigen.
Several problems occur in immunization, however. (1) the response is not always predictable: either immune stimulation or tolerance can be induced; (2) the response to a given antigen preparation in a given host species (e.g. human being, domestic animal, or laboratory animal) can vary greatly from individual to individual; (3) some antigens produce no response or weak responses in comparison to other antigens (4) the response may In particular, many highly purified bacterial and viral components are weak antigens. There is a particular need to overcome this problem since advances in molecular biology can now make available small and highly purified antigenic components of pathogenic organisms.
Two methods are used to partially overcome the above described problems: carriers and adjuvants. These methods are not always clearly distinguished, and the instant invention contains elements of both of these. A carrier is generally a macromolecule to which a hapten (an antigenic determinant which binds to lymphocyte receptor but cannot induce an immune response) is bound; carriers include tetanus toxoid, diphtheria toxoid and purified protein derivatives. An adjuvant enhances an immune response; examples are Freund's adjuvant (used in animal experimentation), and alum (sometimes used in human vaccines). Other adjuvants include SAF-1 (Synthex), Nor-MDP (Ciba-Geigy), Sqaulene, and Zymozan and "iscoms" (immune-stimulating complex). Additional information on adjuvants included within the scope of this invention are found in Adam, Synthetic Adjuvants, Wiley & Sons, 1985.
Novel concepts in adjuvants or improved antibody presentation include the use of lymphokines as adjuvants, the coupling of antigens with antibodies against the surface molecules of antigen presenting cells (e.g. Type II major histocompatibility complex (MHC); B cell surface antibody). Another recent advance in antigen presentation is the use of biodegradable microspheres made of polylactic/polyglycolic acid copolymers to prolong antibody release. These approaches are disclosed in the "Report of a Meeting on Basic Vaccinology" held by the WHO in Geneva, Dec. 8-11, 1987. Similar approaches are disclosed in U.S. Pat. Nos. 4,225,581 and 4,269,821.
It has been suggested that porous collagen-glycosaminoglycan (collagen-GAG) can be used as a microsphere carrier for the controlled release of antigen or attenuated microorganisms. The porous collagen-GAG can be used to immobilize microorganisms in the pores by physical entrapment or chemical crosslinking; other antigens can be chemically crosslinked to the porous matrix. These microspheres can thus be used as biodegradable vehicles for the antigens. A possible disadvantage of collagen as a material to form microspheres in comparison with certain synthetic materials such as polylactic acid/polyglycolic acid copolymers is the endogenous antigenicity of collagen. Such macroporous microspheres may range from 1 .mu.m to about 1000 .mu.m. A preferred particle size for such a microsphere would be less than about 50 .mu.m to enable the adjuvant to be delivered by injection. For introduction of microorganisms into a preformed microsphere, a desired pore size would be in the micron range; for immobilization of molecular antigens, submicron pore sizes would be appropriate.
A similar controlled release experimental vaccine for rabbits has made by co-polymerizing virus particle and virus subunits into rabbit serum albumin beads (Martin, M.E. et al., Vaccine, 1988 February 6(1). p 33-8).
For induction of tolerance, experiments are underway in which microspheres of porous collagen-chondroitin-6-sulfate (C6S) (obtained from Biomat Corporation) of about 500 .mu.m diameter and with mean pore sized of about 20 m near the surface and of about 50-80 .mu.m in the interior are seeded with bone marrow cells from a donor animal. These microspheres are implanted into a host animal, which is also treated with an antilymphocyte serum. This process is intended to induce tolerance in the host so that an organ can also be transplanted from that donor to that host without rejection by the host animal. This procedure can be distinguished from the application of the instant invention in the induction of tolerance as its sole application to organ transplantations and in its specific use of bone marrow cells as well as antilymphocyte serum. Also, the antigens are not crosslinked to the collagen-GAG matrix.
Biodegradable microspheres can help in the presentation of antigen, for example by prolonging delivery, but they do not enhance or direct the cellular interactions underlying immune response, which is an objective of this invention.